Inflammation - Introduction
Introduction
Inflammation is the process by which cells and exudate accumulate in irritated tissues and usually tend to protect them from further injury.
Cardinal Signs
The classical gross signs of inflammation have been recognised since the time of Celsus (25BC-AD50). These are now known as the cardinal signs of inflammation.
- Reddening (rubor)
- Caused by increased blood flow (hyperaemia) to the area, due to dilation of previously inconspicuous capillaries.
- Swelling (tumour)
- The inflamed area appears swollen due to exudation of fluid from the dilated blood vessels into the inflamed tissue.
- Heat (rubor)
- There is increased heat in the affected tissue due to increased blood flow.
- The temperature of the inflamed portion approximates to internal body temperature.
- Pain (dolor)
- Chemical mediators of pain are released by damaged tissue.
- Inflammatory exudate puts local pressure on nerve endings.
- Loss of function
- The pain and damage to the tissue result in a reluctance to use the inflamed portion.
Causes
There are many causes of inflammation. It can happen due to infiltration of microorganisms and helminths (parasites); to trauma; to some mechanical, thermal, and chemical agents; to some immune reactions; to hypersensitivity/ allergy; and to malignant neoplasms. Each of these causes, although exhibiting symptoms that are very similar, have very different mechanisms to starting inflammation. The outcome of inflammation can also vary considerably, with the best outcome being resolved, acute inflammation, with the worst being continuing, chronic inflammation.